Thermal analysis, nuclear magnetic resonance spectroscopy, and impedance spectroscopy of N,N-dimethyl-pyrrolidinium iodide: An ionic solid exhibiting rotator phases

Abstract

Nuclear magnetic resonance studies on the rotational and translational motions of ionic liquids composed of 1-ethyl-3-methylimidazolium cation and bis (trifluoromethanesulfonyl) N,N-dimethyl-pyrrolidinium iodide has been investigated using differential scanning calorimetry, nuclear magnetic resonance ͑NMR͒ spectroscopy, second moment calculations, and impedance spectroscopy. This pyrrolidinium salt exhibits two solid-solid phase transitions, one at 373 K having an entropy change, ⌬S, of 38 J mol −1 K −1 and one at 478 K having ⌬S of 5.7 J mol −1 K −1 . The second moment calculations relate the lower temperature transition to a homogenization of the sample in terms of the mobility of the cations, while the high temperature phase transition is within the temperature region of isotropic tumbling of the cations. At higher temperatures a further decrease in the 1 H NMR linewidth is observed which is suggested to be due to diffusion of the cations.

Plastic crystal behaviour in tetraethylammonium dicyanamide

“…This linewidth is dominated by very short interactions; the interaction within 1 single static methyl group gives a theoretical linewidth of ∼ 60 kHz. This has been seen for other related compounds, based on the cation dimethyl pyrrolidinium (p 1 [22,38]. All of the examples mentioned above have methyl groups attached directly to quaternary nitrogen, and do not have longer, flexible carbon chains.…”

“…Plastic crystal behaviour requires the mechanical deformation of a material, most likely as a result of slip or dislocation movement. The phase transitions often observed in these types of materials may also be representative of the transition from ordered crystal to rotator phases [21,22]. The link between plastic properties and rotational disorder (as in rotator phases) is currently unclear.…”

“…The increases in entropy and volume accompanying these transitions are such that the remaining entropy of fusion is quite small. N,N′ dimethyl pyrrolidinium iodide ([C 1 mpyr][I]) [22] and N,N′ dimethyl pyrrolidinium bis(trifluoromethylsulfonyl) amide ( ] analogue, for example, led to more significant plastic behaviour and accompanying transport properties such as conductivity. In the case of tetramethylammonium dca [23] the 1 H NMR second moment measurements clearly indicated an onset of diffusion at the highest temperature solid-solid phase transition.…”

Proton transport in choline dihydrogen phosphate/H3PO4 mixtures

“…The solid phases of many ionic liquids have either rotator phases [27][28][29][30][31][32] or plastic crystal phases [33][34][35][36][37][38] in which one or more of the ions undergo rotation and/or translational motion, yielding quite high ionic conductivities in the solid state. Doping of small ions into these solid-state matrices has been shown to increase the ionic conductivity.…”

Organic ionic plastic crystal electrolytes; a new class of electrolyte for high efficiency solid state dye-sensitized solar cells

“…Finally, [C 1 mpyr][I] was included to allow assessment of the performance of an iodide-based salt, and this material displays rotator phases and a solid-solid phase transition before melting. 47 For the utilization of these materials as DSSC electrolytes, the traditional DSSC additives were used; , but all of the electrolytes remain in the solid state over a suitably wide temperature range. For example, the best performing electrolyte, [C 1 mpyr][N(CN) 2 ], has a melting point of 87 C, above which point it becomes an ionic liquid.…”